The present invention relates to imaging three-dimensional voxel data. In particular, the invention relates to the imaging of three-dimensional voxel data with respect to a desired viewpoint and view direction.
The imaging of three-dimensional objects is often referred to as volume rendering. Volume rendering finds applications in many fields. One such field is the rendering of medical data resulting, for example, from the scanning of the human or animal body using computer tomographs and other X-ray scanners, nuclear magnetic resonance scanners and ultrasound scanners, to name but a few examples.
The three-dimensional voxel data generated by modern scanning equipment can be very detailed and complex to interpret. For a physician to be able to make effective use of such scan data, it is desirable to provide tools that can readily be manipulated in real-time. A physician may wish to render the data from different directions and from different positions with respect to the scanned object in order to be able to analyse the scanned object and to detect, for example, abnormalities. The physician may wish to simulate rotation of the scanned object or navigation through the scanned object, generating images in real-time as the translations and rotations are effected. In order to provide relatively smooth motion effects, and simply to provide effective response times, rapid real-time rendering is desirable. Also, it is desirable to enable such rapid, real-time rendering on conventional computer workstations, for example a personal computer.
Many techniques are known for rendering three-dimensional voxel data.
One such technique employs a rotate-warp algorithm [1].
Another such technique [2] employs a shear-warp algorithm and is known as shear-warp factorisation. In this approach, a viewing transformation matrix is factorised into a 3D shear that is parallel to slices of a reference volume an a 2D warp to produce a projection of the sheared volume. Although the shear-warp factorisation provides for relatively efficient three-dimensional rendering when the object is viewed from certain directions, the processing is significantly slower from other viewing directions.
Accordingly, an object of the present invention is to provide improved rendering of three-dimensional objects that can provide rendering that is generally faster and less direction-dependent than conventional shear-warp processing, and preferably permits real-time rendering on conventional personal computer hardware.